1. Field of the Invention
The present invention relates to vibratory strings or music wire for musical instruments such as pianos, guitars, violins and the like, and, in particular, to a novel vibratory string having improved harmonic and tonal stability characteristics.
2. Description of the Related Art
Most music enthusiasts will readily agree that there are few musical experiences more beautiful or fulfilling than listening to music performed on an acoustic instrument such as a grand piano, guitar or violin. The tonal quality, tenor and delicate harmonics of such traditional acoustic instruments have been unsurpassed even by the recent advent of modern digital/electronic sampling and reproduction techniques. However, as improvements and advancements in electronic sound reproduction continue, more and more musicians and music hobbyist are choosing to purchase and play digital electronic keyboard instruments rather than their acoustical piano counterparts.
In part, this shift in consumer preferences can be attributed to the relative inexpense of such electronic instruments, the diversity of sound reproduction and amplification achieved and the ready portability of such instruments. However, another important consideration is that electronic instruments, unlike their acoustic counterparts, generally do not require periodic tuning and maintenance. Anyone who has owned or played an acoustic piano knows that the piano must be periodically tuned by a skilled piano technician in order to keep it in optimal playing condition.
A typical grand piano includes a plurality of longitudinally arranged vibratory strings or wires of varying length overlying a plurality of hammers. The number of strings per note will vary, depending upon the desired pitch of the note, i.e., typically one string per note in the lower octaves and two or three strings per note in the mid and upper octaves. Each string is vibrationally fixed or grounded at one end by a hitch pin located on the bowed portion of the piano harp and, at the other end, by an adjustable tuning pin frictionally and rotatably retained in a tuning ("pin") block. The strings are placed under tension by turning or adjusting the tuning pin so that when a string (or strings) is struck by an associated hammer the string is set into mechanical vibration whereby a sound having a particular desired pitch is produced. The pitch of the sound produced depends largely upon the active length of the string, its weight or mass and the amount of tension applied. Thus, the shorter, smaller diameter strings located at the treble end of a piano typically produce a relatively high pitched sound whereas the longer, larger diameter strings disposed at the bass end of the keyboard produce a much lower pitched sound.
A sound board, typically formed from laminated or glued strips of a light hardwood such as spruce, is disposed underneath the vibratory strings in order to acoustically amplify the vibrations of the activated string or strings into audible sound. The sound board includes one or more bridges, typically of hard rock maple, on which each string bears down. The distance between the bridge and the tuning pin defines the active length of the string. The sound board is typically crowned such that it bows slightly upward pressing the bridge (or bridges) into the taught strings. This configuration has been demonstrated to improve the acoustic qualities of the piano and also helps the sounding board support the immense downward pressure brought to bear against it by the tensioned strings. Because the amount of the required tension can easily attain 100 kg. (220 pounds) or more per string and because many such strings are required to construct a piano of adequate tonal range, most pianos are provided with very sturdy frames and supports to support and secure such strings. Modern grand pianos utilize a heavy cast iron frame or harp so that heavier strings can be used at higher tensions to produce a fuller and richer piano sound.
In addition to the length and diameter of string involved, the tonal qualities of the sound produced when striking a particular string are also dependent upon a number of other factors. These include the particular mechanical properties of the material or materials comprising the string, such as ductility, tensile strength, elasticity and density per unit length. These properties can effect the tonal quality, tenor and dwell of a particular note played, as well as the occurrence or selected amplification or attenuation of various harmonic partials.
A "partial" is a component of a sound sensation which may be distinguished as a simple sound that cannot be further analyzed by the ear and which contributes to the overall character of the complex tone or complex sound comprising the note. The fundamental frequency of the string is the frequency of the first partial, or that frequency caused by the piano string vibrating in the first mode, or the lowest natural frequency of free vibration of the string. A harmonic is a partial whose frequency is usually an integer multiple (eg., n=1, 2, 3 . . . ) of the frequency of the first partial or fundamental frequency of the string.
As noted above, strings for musical instruments are required to keep strong tension and a high degree of stability for a long period of time due to the nature of strings being strung and then tuned. Strings which plastically deform or stretch by bowing, plucking or striking are typically not used on musical instruments because they typically lack sufficient elastic compliance to sustain vibratory motion for any useful period of time and can also deform or permanently stretch if struck or plucked to hard. Conventional vibratory strings used on musical instruments are typically made of materials having a high elastic modulus such as carbon steel wire, stainless steel wire, phosphor bronze wire, synthetic resin, sheep gut, etc. For pianos and guitars, often a carbon steel wire core having a diameter of about 0.090 inches will be wound with annealed copper wire or other precious or semi-precious metals in order to change the density per unit length of the string and to enable optimal adjustment of sound quality, attenuation rate and selection of the basic vibration frequency. Thus, U.S. Pat. No. 5,578,775 to Ito describes a vibratory string for use on musical instruments comprising a core wire composed of long filaments of steel wire, sheathed with a thick mantle of a precious metal such as gold, silver, platinum, palladium, copper, or the like. U.S. Pat. No. 3,753,797 to Fukuda describes an improved string for a stringed instrument comprising carbon steel wire electrically heat treated under tensile stress to reduce residual stress in the string and thereby minimize tonal variation over long periods of time after the string has been strung in the instrument.
Notwithstanding the significant improvements in vibratory strings over the years, it is well know that even a very small change in the stretch or amount of tension on a conventional vibratory string can result in a significant detuning of the string. Such changes may result from, inter alia, environmental conditions, such as temperature, humidity and the like, which cause portions of the sound board, bridge and/or harp to expand or contract and thereby alter the string length/tension. These changes can cause the piano or other string instrument to produce a less than optimum sound, especially if a rather large change is experienced. Also, during the initial tuning of the piano by factory personnel, the tensioning or de-tensioning of the various strings can cause similar changes in the shape of the sound board, bridge and/or harp, particularly the degree of crowning of the sound board. The latter is directly affected by the total amount of downward pressure exerted on the sound board by the strings under tension. Thus, repeated iterative tuning at the factory over the course of several days or weeks is often necessary to achieve a desired stable tonal range.
Even after a piano is put into service, periodic adjustment and maintenance by a skilled piano technician is required to keep the strings optimally tuned. This is typically effected by turning the various tuning pins, either tightening or loosening each associated string. Repeated adjustment of the tuning pins over years of use tends to adversely affect the tuning pins and/or the tuning block in which they are frictionally retained. As a result, the pin block of an older piano will often become so worn by repeated tunings that the tuning pins no longer have sufficient frictional engagement with the pin block to prevent them from rotating under the residual stress of the tuned string. In such case the piano will not be able to hold its tune for prolonged periods and must either be tuned much more frequently or the pin block must be repaired or replaced.
Furthermore, those skilled in the art will appreciate that when a vibratory string is struck, plucked, bowed or otherwise excited, the transient vibratory displacement (and, therefore, stretching) of the string itself can effectively increase the natural pitch of the string for higher harmonic partials. This is because as the string vibrates at the fundamental and lower harmonics it must necessarily increase its length by periodically stretching and contracting as the string moves back and forth during the resultant transient decay. Effectively, this increases the tension on the string and, therefore, undesirably increases the pitch of higher harmonic partials. Thus, these higher harmonic partials can actually vibrate in disharmony with the fundamental and lower harmonic partials, causing unpleasant overtones, particularly in the seventh, ninth and higher harmonics.
Conventionally, piano manufacturers have attempted to compensate for these unpleasant overtones by carefully selecting the strike point of the hammer so that it falls on or near a node of the partial harmonic(s) desired to be attenuated. See, for example, U.S. Pat. No. 4,244,268 to Barham. However, such approaches have been unsuccessful in removing all of the undesired disharmonic overtones. Rather, they are only compromise approaches which attempt to attenuate as much as possible those disharmonic overtones that the human car finds most unpleasant.